I don't think the Colt ambidextrious safety requires the right grip panel to be relieved. What Colt (actually subcontracted out to Menscke) did was to mill a lip along the edge of the left thumb safety. A longer sear pin with a dovetail cut is used to engage that milled lip, thereby preventing the left thumb safety from walking out of the gun. For me, it's easily the best there is. Not fancy, but darn clever.
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